Bone fixing material

ABSTRACT

Provided is a bone fixation material that does not deteriorate in properties even by an electron beam sterilization treatment performed before or during use as a bone fixation material, has fatigue resistance, wear resistance, and dimensional stability at excellent levels, also has biocompatibility, and offers excellent osteoconnectivity. The bone fixation material according to the present invention includes a nonwoven fabric made of PEEK fibers. The bone fixation material according to the present invention preferably has an average pore size of 3 to 280 μm and preferably has a porosity of 15% to 70%. The PEEK fibers preferably have an average fiber diameter of 10 μm or less.

TECHNICAL FIELD

The present invention relates to bone fixing materials (bone fixationmaterials) for use in the medical field. This application claimspriority to Japanese Patent Application No. 2016-249366, filed to Japanon Dec. 22, 2016, the entire contents of which are incorporated hereinby reference.

BACKGROUND ART

Conventionally, in the medical field, bone fixation materials have beenused for the purpose of repairing, reinforcing, and/or protecting injuryareas typically in the bone tissue, where the injury has been causedtypically by a disease or in an accident. The bone fixation materialsare used by enveloping or covering such a bone injury area, or byenveloping or covering an artificial bone or by being incorporated intoan artificial bone. Non-limiting examples of the artificial bone includenon-resorbable materials (such as HAP), resorbable materials (such asβ-TCP), and setting materials (such as α-TCP), which augment a boneinjury portion. The bone fixation materials are implanted in, and remainin a living body without in-vivo decomposition and absorption andtherefore require biological functions such as osteoconnectivity andbiocompatibility. The bone fixation materials also require suchdurability as to resist deterioration over a long duration.

Conventionally used materials to form the bone fixation materials asabove are resins such as polyacrylonitriles, poly(ether ketone)s,polyimides, aromatic polymers, and aliphatic polymers (PTL 1).

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication (JP-A)(Translation of PCT Application) No. 2007-533371

SUMMARY OF INVENTION Technical Problem

The resins described in PTL 1, however, disadvantageously deteriorate inproperties when subjected to electron beam sterilization treatmentbefore or during use as bone fixation materials. In addition, theseresins do not always have good biocompatibility.

Accordingly, the present invention has an object to provide a bonefixation material that does not deteriorate in properties even byelectron beam sterilization treatment performed before or during use asa bone fixation material, has not only fatigue resistance, wearresistance, and dimensional stability at excellent levels, but alsobiocompatibility, and offers excellent osteoconnectivity.

Solution to Problem

After intensive investigations to achieve the object, the inventors ofthe present invention found that a bone fixation material that achievesthe object can be prepared using a nonwoven fabric made of poly(etherether ketone) (PEEK) fibers. The present invention has been made on thebasis of these findings.

Specifically, the present invention provides a bone fixation materialincluding a nonwoven fabric made of PEEK fibers.

The bone fixation material according to the present invention preferablyhas an average pore size of 3 to 280 μm.

The bone fixation material according to the present invention preferablyhas a porosity of 15% to 70%.

The PEEK fibers in the bone fixation material according to the presentinvention preferably have an average fiber diameter of 10 μm or less.

In the bone fixation material according to the present invention, thenonwoven fabric preferably has a mass per unit area of 10 to 100000g/m².

In the bone fixation material according to the present invention, thenonwoven fabric preferably has a thickness of 0.05 to 100 mm.

The PEEK fibers in the bone fixation material according to the presentinvention preferably have a degree of crystallinity of 30% or less.

Advantageous Effects of Invention

The bone fixation material according to the present invention is mademainly of PEEK, thereby does not deteriorate in properties even byelectron beam sterilization treatment performed before or during use asa bone fixation material, has fatigue resistance, wear resistance, anddimensional stability at excellent levels, offers dynamiccharacteristics similar to those of the bone, and also hasbiocompatibility. The bone fixation material according to the presentinvention includes PEEK fibers, or a nonwoven fabric made of PEEKfibers, thereby also has excellent osteoconnectivity, and readilyadheres to the bone. This offers an expectation of early boneregeneration. The bone fixation material according to the presentinvention uses PEEK fibers, thereby is very flexible, and is free fromfear of damage on bone or surrounding soft tissues. The bone fixationmaterial according to the present invention uses PEEK fibers, therebydoes not form sharp pieces, and lightly affects the human body. The bonefixation material has both strength and flexibility and thereby iscapable of undergoing shape correction in situ in an operation. Inaddition, the bone fixation material according to the present inventionis not absorbed into the body, and this can eliminate or minimizeadhesion typically to the internal organs after operation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of a PEEK fiber production methodaccording to an embodiment;

FIG. 2 is a schematic view of Taylor cones formed in a band-like meltzone;

FIG. 3 is a schematic cross-sectional view of nonwoven fabric productionequipment according to an embodiment, which employs or includes the PEEKfiber production method;

FIG. 4 schematically illustrates how to use the bone fixation materialaccording to the present invention, in an embodiment where the bonefixation material is tubular; and

FIG. 5 schematically illustrates how to use the bone fixation materialaccording to the present invention, in an embodiment where the bonefixation material is sheet-like.

DESCRIPTION OF EMBODIMENTS

Bone Fixation Material

The bone fixation material according to the present invention serves asa bone reinforcer (bone protector). The bone fixation materialcharacteristically includes PEEK fibers, or a nonwoven fabric made ofPEEK fibers. The bone fixation material is in the form of, for example,a sheet or a tube (cylinder) and is a porous material having amultiplicity of pores. How to use the bone fixation material accordingto the present invention is illustrated in FIG. 4 in an embodiment wherethe material is tubular; and is illustrated in FIG. 5 in an embodimentwhere the material is sheet-like. It is also acceptable that asheet-like bone fixation material is shaped into a tube (cylinder)before or during use. The bone fixation material according to thepresent invention is used typically as covering a bone lesion area.

The bone fixation material has an average pore size of typically 3 to280 μm, preferably 5 to 260 μm, more preferably 10 to 240 μm, andfurthermore preferably 20 to 220 μm. The bone fixation material, whenhaving an average pore size within the range, allows neoplasticosteoblasts to readily enter and grow in the pores, to become readilyintegrable with the bone tissue, and to easily adhere to the bone. Thisoffers an expectation of early bone regeneration. The average pore sizecan be measured typically by measuring sizes of pores as observedtypically in an electron photomicrograph, and determining the average ofthe measured pore sizes.

The bone fixation material has a porosity (pore content) of typically15% to 70%, preferably 20% to 65%, and more preferably 25% to 60%. Thebone fixation material, when having a porosity within the range, allowsneoplastic osteoblasts to readily enter and grow in the pores, to becomereadily integrable with the bone tissue, and to easily adhere to thebone. This offers an expectation of early bone regeneration. Theporosity can be measured by determining the area of pores per unit areaas observed using an electron photomicrograph.

The bone fixation material according to the present invention has athickness of typically about 0.05 to about 100 mm, preferably 0.1 to 50mm, more preferably 0.2 to 20 mm, and furthermore preferably 0.3 to 10mm. The bone fixation material has a density of typically about 0.05 toabout 1.2 g/cm³, preferably 0.1 to 1.0 g/cm³, and more preferably 0.2 to0.8 g/cm³. The bone fixation material according to the present inventionmay have any size as long as being such a size as to cover the bonelesion area. The bone fixation material, when being in the form ofsheet, may have a length of one side of the sheet of typically 10 to 600mm, and preferably 50 to 400 mm.

The bone fixation material according to the present invention is notparticularly limited, as long as including a nonwoven fabric made ofPEEK fibers. The content of the nonwoven fabric made of PEEK fibers istypically 50 weight percent or more, preferably 70 weight percent ormore, more preferably 80 weight percent or more, and furthermorepreferably 90 weight percent or more, of the totality of the bonefixation material. In addition to the nonwoven fabric made of PEEKfibers (PEEK fiber nonwoven fabric), the bone fixation material mayfurther include any of other components such as other thermoplasticresins, thermosetting resins, metals, and ceramics, within such rangesas not to adversely affect the advantageous effects of the presentinvention.

The bone fixation material according to the present invention may besubjected to hydrophilization treatment for the purpose of surfacemodification. The hydrophilization treatment allows the bone fixationmaterial to have a finer porous structure at its surface. Non-limitingexamples of the hydrophilization treatment include plasma treatment,graft reaction after plasma treatment, corona discharge treatment, glowdischarge treatment, alkaline solution treatment, acid solutiontreatment, oxidizer treatment, silane coupling treatment, anodizingtreatment, and roughening treatment. Among them, plasma treatment, graftreaction after plasma treatment, and corona discharge treatment aretypified.

The plasma treatment is performed typically by applying microwave plasmato the surface of the bone fixation material in the atmosphere (air)using a microwave plasma processor. Assume that the microwave plasmaprocessor is a scanning-and-processing device in which a sample passesimmediately below the plasma reactor at a uniform velocity. In thiscase, the travel speed (feed speed) of the sample is generally about 1to about 20 m/min. Non-limiting examples of the (gas) plasma includeoxygen, nitrogen, argon, and hydrogen. Instead of the air atmosphere,the plasma treatment may also be performed in another atmosphere such asnitrogen or argon atmosphere, or in a vacuum. A non-limiting example ofthe microwave plasma processor for use herein is a microwave plasmaprocessor (microwave plasma system) supplied by Nissin Inc.

The graft reaction after plasma treatment is performed typically byimmersing the bone fixation material after the plasma treatment in anacrylic acid substance such as methyl acrylate or ethyl acrylate in anatmosphere typically of nitrogen or argon for reaction with the acrylicacid substance. The graft reaction can further modify (hydrophilize) thesurface of the porous shaped article. The acrylic acid substance for useherein may be a solution resulting from moderate dilution of thesubstance with an organic solvent such as toluene. The immersion isgenerally performed for about 1 to about 48 hours and may be performedat room temperature or at a temperature of about 30° C. to about 80° C.

The corona discharge treatment is performed typically by applying coronadischarge electrons to the surface of the bone fixation material, wherethe electrons result from corona discharge in the atmosphere (air) usinga corona discharge surface treatment system. When the corona dischargesurface treatment system employs a conveyor system, the feed speed ofthe conveyor is generally about 1 to about 20 m/min, and the coronadischarge is performed at an output of generally about 30 to about 500W. A non-limiting example of the corona discharge surface treatmentsystem for use herein is a corona discharge surface treatment systemsupplied by WEDGE Co., Ltd.

The bone fixation material according to the present invention may besubjected to Ca²⁺ treatment by immersing the same in an aqueous solutiontypically of calcium hydroxide (Ca(OH)₂), calcium dihydrogenphosphate(Ca(H₂PO₄)₂), or calcium chloride (CaCl₂). The immersion may beperformed for a duration of typically 1 to 30 days, and preferably 3 to20 days. The Ca²⁺ treatment allows the bone fixation material to morereadily bear apatite formed on the surface thereof and to more readilyhave better osteoconductivity.

PEEK Fibers

The PEEK fibers are preferably fibers having small fiber diameters andmay have diameters of typically 10 μm or less (0.1 to 10 μm). The PEEKfibers have diameters of preferably 0.5 to 8 μm, and more preferably 0.7to 6 μm. The fibers having diameters as above may include fine fibershaving fiber diameters of typically about 50 to about 1000 nm. Thediameters of the PEEK fibers can be adjusted by appropriately adjustingconditions for the after-mentioned PEEK fiber production method, such aspolymer sheet thickness, polymer sheet feed speed, and laser intensity.The diameters of the PEEK fibers can be measured typically using anelectron microscope.

The PEEK fibers, when considered as an assembly, have an average fiberdiameter (average diameter) of typically 10 μm or less (0.1 to 10 μm),preferably 0.5 to 8 μm, and more preferably 0.7 to 6 μm. The averagefiber diameter can be determined typically by taking two or more (e.g.,ten) images of shapes of fibers using a scanning electron microscope;measuring diameters of about ten fibers per image optionally selectedfrom the images, typically using image processing software; andaveraging the measured diameters.

The PEEK fibers have a degree of crystallinity of typically 30% or less,preferably 29% or less, and more preferably 28% or less. The PEEKfibers, when having a degree of crystallinity of 30% or less, offerexcellent workability and can be readily shaped into a nonwoven fabric.The degree of crystallinity can be determined by a technique such asX-ray diffractometry, differential scanning calorimetry (using adifferential scanning calorimeter; DSC), or densimetry. The degree ofcrystallinity is a value calculated from the amount of heat (calorie)determined by differential scanning calorimetry (DSC) by a methoddescribed in a working example.

The PEEK fibers include PEEK in a proportion of typically 50 weightpercent or more, preferably 70 weight percent or more, more preferably80 weight percent or more, and furthermore preferably 90 weight percentor more, of the totality of the PEEK fibers. Particularly preferably,the PEEK fibers are made of PEEK alone. The PEEK fibers may include anyof other components such as other thermoplastic resins and additives, inaddition to PEEK. The PEEK fibers are preferably prepared using theafter-mentioned polymer sheet as a starting material, by theafter-mentioned PEEK fiber production method.

Nonwoven Fabric

The nonwoven fabric is a sheet-like assembly of the PEEK fibers. Thethickness of the nonwoven fabric may be selected within the range oftypically about 0.05 to about 100 mm according to the intended purpose,but is preferably 0.1 to 50 mm, more preferably 0.2 to 20 mm, andfurthermore preferably 0.3 to 10 mm. The nonwoven fabric has a mass perunit area (METSUKE) of typically about 10 to about 100000 g/m²,preferably 20 to 20000 g/m², and more preferably 50 to 10000 g/m². Thegeometries or dimensions, such as fiber diameter, thickness, and massper unit area, of the nonwoven fabric to be produced can be controlledby adjusting conditions such as sheet feed speed, laser intensity, aswell as collection member traveling speed in the after-mentionednonwoven fabric production method.

The nonwoven fabric may include the PEEK fibers in a content oftypically 50 weight percent or more, preferably 70 weight percent ormore, more preferably 80 weight percent or more, and furthermorepreferably 90 weight percent or more, of the totality of the nonwovenfabric. The nonwoven fabric may further include other components inaddition to the PEEK fibers, within ranges not adversely affecting theadvantageous effects of the present invention. Non-limiting examples ofthe other components include other thermoplastic resins, thermosettingresins, metals, and ceramics.

Bone Fixation Material Production Method

The bone fixation material according to the present invention may beobtained typically, but non-limitingly, by producing PEEK fibers, andproducing a nonwoven fabric from the PEEK fibers. Hereinafter, the PEEKfiber production method, and the PEEK fiber nonwoven fabric productionmethod will be described.

PEEK Fiber Production Method

The PEEK fibers can be produced typically, but non-limitingly, by alaser melt electrospinning technique. Namely, the PEEK fibers may be,for example, laser melt electrospun PEEK fibers. According to the PEEKfiber production method, the PEEK fibers are produced in the followingmanner. Planar laser light (laser sheet) is applied to a polymer sheetto heat and melt an edge of the polymer sheet linearly to thereby form aband-like melt zone. With this, a potential difference is appliedbetween the band-like melt zone and a fiber collector to form needleprotrusions in the band-like melt zone of the polymer sheet and to allowfibers ejected from the needle protrusions to fly toward the fibercollector. The fibers are collected on the fiber collector or on acollection member disposed between the band-like melt zone and the fibercollector, to give the PEEK fibers.

The laser melt electrospinning technique will be illustrated withreference to the attached drawings. FIG. 1 is a schematic illustrationof the PEEK fiber production method according to an embodiment.

In the PEEK fiber production method as illustrated in FIG. 1, laserlight having a spot cross section emitted from a laser source 1 isconverted into planar laser light 5 having a linear cross section, bythe working of a light-path controller. The light-path controllerincludes a beam-expander-homogenizer 2, a collimation lens 3, and acylindrical lens group 4. The planar laser light 5 is applied to an edgeof a polymer sheet 6 held by a holder 7, to form a band-like melt zone 6a. With this, a voltage is applied from a high voltage generator 10 toform a potential difference between the band-like melt zone 6 a and afiber collector 8 disposed under the polymer sheet 6. A thermography 9observes the temperature of the band-like melt zone 6 a so as tooptimize conditions such as the voltage and the laser light to beapplied.

In the embodiment illustrated in FIG. 1, the holder 7, which holds thepolymer sheet 6, functions also as an electrode and, when receives thevoltage from the high voltage generator 10, imparts an electric chargeto the band-like melt zone 6 a of the polymer sheet 6, where the meltzone 6 a is formed by the application of the planar laser light 5. Thefiber collector 8 has a surface electric resistance approximatelycomparable to those of metals. The fiber collector 8 may have a shapeselected typically from plate, roller, belt, net, sawlike, wave, needle,and linear shapes.

FIG. 2 is a schematic view of Taylor cones formed in the band-like meltzone 6 a. As illustrated in FIG. 2, at the surface of the band-like meltzone 6 a to which electric charges are applied, needle protrusions(Taylor cones) 6 b are gradually formed due to building up and repellingof the electric charges on the surface. When the repulsive force of theelectric charges exceeds the surface tension, the molten polymer sheetis ejected as fibers from the tips of the Taylor cones toward the fibercollector 8 by the action of electrostatic attraction. Namely, fibersare formed from the needle protrusions 6 b and fly toward the fibercollector 8. As a result, the fibers elongate and are collected by thefiber collector 8. In an embodiment, a collection member is disposed onor over the fiber collector 8. In this embodiment, the fibers arecollected on the collection member. Specifically, in the PEEK fiberproduction method, a member for collecting fibers may be the fibercollector itself, or not the fiber collector, but a collection member(collecting member) disposed on or over the fiber collector.

The number of the Taylor cones (spacing between Taylor cones) asillustrated in FIG. 2 can be controlled by changing the thickness of thepolymer sheet 6 as appropriate. The “growth” of a Taylor cone refers toincrease in height (h in FIG. 2) of the Taylor cone.

The number of the Taylor cones is not particularly limited, butpreferably 1 to 100, more preferably 1 to 50, and furthermore preferably2 to 10, per 2 cm in the width direction of the heated, melt zone of thepolymer sheet. When Taylor cones are present in a number of 1 to 100 per2 cm in the width direction, the fibers can be surely produced in anappropriate production volume without decrease in fiber uniformity ratiocaused typically by electric repulsion between the Taylor cones.

Non-limiting examples of the laser source include YAG laser, carbondioxide gas (CO₂) laser, argon laser, excimer laser, and helium-cadmiumlaser. Among them, carbon dioxide gas laser is preferred because ofhaving high power-supply efficiency and high capability of melting PEEKresins. The laser light may have a wavelength of preferably about 200 nmto about 20 μm, more preferably about 500 nm to about 18 μm, andfurthermore preferably about 5 to about 15 μm.

The laser light, when to be applied as planar laser light in the PEEKfiber production method, preferably has a thickness (plane thickness) ofabout 0.5 to about 10 mm. The laser light, if having a thickness of lessthan 0.5 mm, may fail to invite the formation of Taylor cones. The laserlight, if having a thickness of greater than 10 mm, may causedeterioration of the material because of longer residence time duringmelting.

The power (output) of the laser light may be controlled within such arange that the band-like melt zone has a temperature equal to or higherthan the melting point of the polymer sheet and equal to or lower thanthe ignition point of the polymer sheet. The power is preferably highfrom the viewpoint of allowing the ejected PEEK fibers to have smallfiber diameters. The specific power of the laser light can be selectedas appropriate according typically to properties (such as melting pointand limiting oxygen index (LOI)) and shape of the polymer sheet to beused, and to the feed speed of the polymer sheet. The power ispreferably about 5 to about 100 W per 13 cm, more preferably 20 to 60 Wper 13 cm, and furthermore preferably 30 to 50 W per 13 cm. The power ofthe laser light is the power (output) of an outgoing spot beam from thelaser source.

The temperature of the band-like melt zone is not particularly limited,as long as being equal to or higher than the melting point (334° C.) ofPEEK and equal to or lower than the ignition point of PEEK, but isgenerally about 350° C. to about 600° C., and preferably 380° C. to 500°C.

In the PEEK fiber production method illustrated in FIG. 1, the laserlight is applied from only one direction to the band-like melt zone(edge) of the polymer sheet. In another embodiment, the laser light maybe applied typically from two directions with a reflective mirror to theband-like melt zone (edge) of the polymer sheet. This configurationcontributes to more uniform melting of the edge of the polymer sheeteven when the polymer sheet has a large thickness.

In the PEEK fiber production method, the potential difference to begenerated between the edge of the polymer sheet and the collectionmember is preferably such a potential difference as to give a highvoltage within a range not causing discharge. The potential differencecan be selected as appropriate according typically to the required fiberdiameter, the distance between the electrode and the collection member,and the irradiance of the laser light, and is generally about 0.1 toabout 30 kV/cm, preferably 0.5 to 20 kV/cm, and more preferably 1 to 10kV/cm.

The voltage may be applied to the melt zone of the polymer sheet by adirect application technique, in which the portion to be irradiated withthe laser light (band-like melt zone of the polymer sheet) is coincidentwith an electrode unit for imparting the electric charges. However, thevoltage is preferably applied by an indirect application technique, inwhich the portion to be irradiated with the laser light is disposed at aposition different from the position of the electrode unit for impartingthe electric charges. The indirect application technique is preferredbecause equipment for this technique can be prepared easily and simply,the laser light can be effectively converted into thermal energy, andthe reflection direction of the laser light can be easily controlled tooffer high safety. Among such indirect application techniques, preferredis a technique in which the portion to be irradiated with the laserlight is disposed downstream from the electrode unit in the feedingdirection of the polymer sheet. In particular, in a preferred embodimentof the production method, the planar laser light is applied to thepolymer sheet downstream from the electrode unit, and the distancebetween the electrode unit and the portion to be irradiated with thelaser light (e.g., the distance between the lower end of the electrodeunit and the upper outer periphery of the planar laser light) iscontrolled within a specific range (e.g., about 10 mm or less). Thisdistance can be selected according typically to the electricconductivity, thermal conductivity, and glass transition point of thepolymer sheet, and the irradiance of the laser light. The distance ispreferably about 0.5 to about 10 mm, more preferably about 1 to about 8mm, furthermore preferably about 1.5 to about 7 mm, and particularlypreferably about 2 to about 5 mm. When the two portions are disposed ata distance within the range, the resin adjacent to the portion to beirradiated with the laser light offers higher molecular mobility and canreceive sufficient electric charges in a molten state. This contributesto better productivity.

The distance between the edge of the polymer sheet (tip of a Taylorcone) and the collection member is not limited and may be generally 5 mmor more. For efficient production of fibers having small diameters, thedistance is preferably 10 to 300 mm, more preferably 15 to 200 mm,furthermore preferably 50 to 150 mm, and particularly preferably 80 to120 mm.

The polymer sheet, when fed continuously, is fed at a feed speed ofpreferably about 2 to about 20 mm/min, more preferably 3 to 15 mm/min,and furthermore preferably 4 to 10 mm/min. The feeding of the polymersheet at a higher speed contributes to higher productivity. However, thefeeding, if performed at an excessively high speed, may impede fiberproductivity due to insufficient melting of the polymer sheet in theportion irradiated with the laser light. In contrast, the feeding, ifperformed at an excessively low speed, may cause decomposition of thepolymer sheet and/or may invite lower productivity.

The polymer sheet has a degree of crystallinity of preferably 25% orless, more preferably 20% or less, and furthermore preferably 15% orless. The polymer sheet, when having a degree of crystallinity of 25% orless, can give PEEK fibers having a low degree of crystallinity. Thedegree of crystallinity of the polymer sheet can be determined by atechnique similar to that for the degree of crystallinity of the PEEKfibers.

The polymer sheet preferably has a low melt viscosity so as to readilygive fibers having small fiber diameters. The melt viscosity of thepolymer sheet is preferably 800 Pa·s or less (50 to 800 Pa·s), morepreferably 600 Pa·s or less, and furthermore preferably 400 Pa·s orless, where the melt viscosity is measured at 400° C. and a shear rate(shearing velocity) of 121.6 s⁻¹. The melt viscosity can be determinedby the method described in the working example, using a capillaryrheometer Capillograph 1D (trade name, supplied by Toyo SeikiSeisaku-Sho, Ltd.). The shear rate can also be measured using such acapillary rheometer.

The polymer sheet can be produced typically by heating, melting, andshaping PEEK in the form of chips into a sheet using a device such as aT-die extruder. The PEEK chips may be available as commercial products,of which one under the trade name of VESTAKEEP 1000G (supplied byDaicel-Evonik Ltd.), for example, is advantageously usable. The heatingtemperature of the T-die extruder has only to be equal to or higher thanthe melting point of PEEK and is typically 350° C. to 400° C.

The polymer sheet may contain any of various additives for use infibers. Non-limiting examples of the additives include infraredabsorbents, stabilizers (such as antioxidants, ultraviolet absorbers,and thermal stabilizers), flame retardants, antistatic agents,colorants, fillers, lubricants, antibacterial agents, insect/tickrepellents, antifungal agents, flatting agents, heat storage media,flavors, fluorescent brighteners, wetting agents, plasticizers,thickeners, dispersants, blowing agents, and surfactants. The polymersheet may contain each of different additives alone or in combination.

Among these additives, a surfactant is preferably used. Assume that ahigh voltage is applied to the polymer sheet to inject electric chargesinto the polymer sheet. In this case, the polymer sheet offers highelectric insulation and it therefore is difficult to inject the electriccharges into a thermally melt zone having a lower electric resistance.However, the use of a surfactant allows the polymer sheet having highelectric insulation to have lower electric resistance in its surface,and this allows the electric charges to be injected sufficiently intothe thermally melt zone. Compounding of an additive such as a surfactantis effective for phase separation of multiple components contained inthe polymer sheet upon application of a high voltage to the polymersheet to inject electric charges into the sheet.

The polymer sheet may contain any of these additives each in aproportion of 50 parts by weight or less, preferably 0.01 to 30 parts byweight, and more preferably 0.1 to 5 parts by weight, per 100 parts byweight of the resin constituting the polymer sheet.

The polymer sheet has a thickness of preferably 0.01 to 10 mm, and morepreferably 0.05 to 5.0 mm. The polymer sheet, when having a thicknesswithin the range, contributes to easy production of the PEEK fibers.

In the PEEK fiber production method, space between the edge of thepolymer sheet and the collection member may be in an inert gasatmosphere. The presence of the inert gas atmosphere in the spacerestrains the ignition of the fibers and allows the laser light to beapplied at a higher power. Non-limiting examples of the inert gasinclude nitrogen gas, helium gas, argon gas, and carbon dioxide gas.Among them, nitrogen gas is generally used. In addition, the use of theinert gas can restrain oxidation reactions in the band-like melt zone.

The space may be heated. The heating allows the resulting fibers to havesmaller diameters. Specifically, heating of the air or inert gas in thespace can restrain abrupt temperature fall of fibers under growing, andthis promotes growth or extension of the fibers to give more ultrafinefibers. The heating may be performed typically by using a heater (suchas a halogen heater) or by applying laser light. The heating temperaturemay be selected typically within the range of from 50° C. to lower thanthe ignition point of the resin. In consideration of spinnability, theheating temperature is preferably lower than the melting point of PEEK.

PEEK Fiber Nonwoven Fabric Production Method

Next, a method for producing a PEEK fiber nonwoven fabric (PEEK fibernonwoven fabric production method) according to an embodiment will beillustrated. By the below-mentioned PEEK fiber nonwoven fabricproduction method a nonwoven fabric is obtained by continuouslyperforming the above-mentioned PEEK fiber production method whilemoving, with time, the position at which the fibers are collected, andcollecting and accumulating the fibers to form a sheet, where the fibershave flown toward the fiber collector. The nonwoven fabric made of PEEKfibers (PEEK fiber nonwoven fabric) may be produced by the methoddescribed below, or by preparing PEEK fibers by the above-mentioned PEEKfiber production method and forming the PEEK fibers into a nonwovenfabric by another technique.

Exemplary techniques for moving with time the position at which thefibers flown toward the fiber collector are collected include (1) thetechnique of moving the collection member (or the fiber collector whenthe fiber collector itself functions as a collection member); (2) thetechnique of moving the position at which the polymer sheet is held; (3)the technique of allowing mechanical, magnetic, or electric force to actupon fibers flying from the Taylor cones toward the collection member,such as the technique of blowing air to the fibers during flying; and(4) a technique as any selective combination of the techniques (1) to(3).

Among them, the technique (1), namely, the technique of moving thecollection member is desirable, because this technique allows easysimplification of the configuration of the equipment and allows easycontrol of the geometries (such as thickness and mass per unit area) ofthe nonwoven fabric to be produced. The PEEK fiber nonwoven fabricproduction method will be illustrated in detail below, by taking aprocedure using the technique (1) as an example.

The PEEK fiber nonwoven fabric production method using the technique (1)may be performed in the following manner. In the PEEK fiber productionmethod illustrated in FIG. 1, a collection member is placed on the fibercollector 8; and, while moving the collection member in a direction(right hand or left hand in the figure) perpendicular to the widthdirection of the polymer sheet 6, the PEEK fiber production method isperformed continuously. The collection member may be moved at a constantspeed, or at a speed varying with time, or may be moved and stoppedrepeatedly. To continuously perform the PEEK fiber production method,the polymer sheet 6 may be continuously fed toward the fiber collector 8(toward the collection member) with the progress of the fiber productionprocess, as has been described above. The speed (feed speed) of thepolymer sheet during the continuous feeding is as described in the PEEKfiber production method.

The moving speed of the collection member on or over the fiber collector8 is not limited, may be selected as appropriate in considerationtypically of the mass per unit area of the fiber sheet to be produced,and is generally about 10 to about 2000 mm/min. For example, assume thata polymer sheet having a mass per unit area of 1000 g/m² is fed at afeed speed of 0.5 mm/min. In this case, a nonwoven fabric having a massper unit area of about 0.5 g/m² can be continuously produced by settingthe moving speed of the collection member at about 1000 mm/min.

FIG. 3 is a schematic cross-sectional view of exemplary nonwoven fabricproduction equipment employing or including the PEEK fiber productionmethod illustrated in FIG. 1. The equipment (nonwoven fabric productionequipment) illustrated in FIG. 3 includes a laser source 11; alight-path controller 12; a polymer sheet feeder 13 capable ofcontinuously feeding the polymer sheet 6; and a cabinet 23. The cabinet23 houses a holder 16 that holds the polymer sheet 6; an electrode 17that applies electric charges to the polymer sheet 6; a collectionmember 22 that collects fibers; a fiber collector 14 that is disposed soas to face the electrode 17 through a band-like melt zone (edge) 6 a ofthe polymer sheet 6 and the collection member 22; and a heating device15. The equipment also includes high voltage generators 20 a and 20 bwhich apply a voltage respectively to the electrode 17 and to the fibercollector 14; and pulleys 21 for moving the collection member 22. Thelight-path controller 12 is an assembly of optical components asdescribed above and includes, for example, the beam-expander-homogenizer2, the collimation lens 3, and the cylindrical lens group 4 asillustrated in FIG. 1.

With reference to FIG. 3, the planar laser light 5, which is emittedfrom the laser source 11 and travels via the light-path controller 12,is introduced into the cabinet 23 and is applied to the band-like meltzone (edge) 6 a of the polymer sheet 6. The polymer sheet feeder 13 ismounted on the upper side of the cabinet 23 and includes a motor, and amechanism that converts the rotation of the motor into a rectilinearmotion. The polymer sheet feeder 13 receives the polymer sheet 6 andcontinuously feeds the same into the cabinet 23. The lower part of thepolymer sheet 6 is held by the holder 16 on which the electrode 17 ismounted. The polymer sheet 6 and the electrode 17 are always in contactwith each other, and thus electric charges are applied to the polymersheet 6 upon application of a voltage to the electrode 17.

The fiber collector 14, which functions as a counter electrode to theelectrode 17, is disposed at such a position as to face the electrode 17through the band-like melt zone (edge) 6 a of the polymer sheet 6 andthe collection member 22. This configuration gives a potentialdifference between the band-like melt zone (edge) 6 a of the polymersheet 6 and the collection member 22 when a voltage is applied betweenthe electrode 17 and the fiber collector 14. The high voltage generators20 a and 20 b are coupled respectively to the electrode 17 and to thefiber collector 14 and apply a voltage between the electrode 17 and thefiber collector 14. In the nonwoven fabric production equipment, theelectrode 17 serves as a positive electrode, and the fiber collector 14serves as a negative electrode. The reverse configuration will also do.The collection member 22 herein is a belt conveyor including the pulleys21 and a conveyor belt, and the conveyor belt itself corresponds to thecollection member 22. Accordingly, the collection member 22 (conveyorbelt) travels to a predetermined direction (e.g., right hand in thefigure) with the driving of the pulleys 21.

The nonwoven fabric production equipment illustrated in FIG. 3 includesthe heating device 15 and can heat and keep warmth of fibers ejected andelongated from the band-like melt zone (edge) 6 a of the polymer sheet 6toward the collection member 22. The equipment also includes a laserlight absorber 19 and a heat absorber 18 in the cabinet 23.

Using the nonwoven fabric production equipment illustrated in FIG. 3, anonwoven fabric is produced in the following manner. While a voltage isapplied between the electrode 17 and the fiber collector 14 and whilethe polymer sheet 6 is fed by the working of the polymer sheet feeder 13and the holder 16, the planar laser light 5 is applied to the band-likemelt zone (edge) 6 a of the polymer sheet 6. This allows Taylor cones toform in the band-like melt zone (edge) 6 a of the polymer sheet 6,allows the formed Taylor cones to eject fibers, and allows the fibers tofly (to be jetted) toward the fiber collector 14. As a result, elongatedfibers are collected by the collection member 22, as has been describedabove. Then, while the polymer sheet 6 is continuously fed (while fibersare continuously ejected), the collection member 22 is moved, to givethe nonwoven fabric on the collection member 22.

The collection member 22 in the nonwoven fabric production equipmentillustrated in FIG. 3 is a sheet-like member. In this equipment, thecollection member 22 is not limited, as long as being in the form ofsheet, but may be made of a material selected typically from paper,films, various woven fabrics, nonwoven fabrics, and meshes. Thecollection member may also be a sheet or belt made of a metal or amaterial having a surface electric resistance comparable to those ofmetals.

In the nonwoven fabric production equipment illustrated in FIG. 3,materials to constitute the electrode 17 and the fiber collector 14 haveonly to be conductive materials (generally, metal components).Non-limiting examples of such materials include elementary metalstypically of Group 6 elements such as chromium; Group 10 elements suchas platinum; Group 11 elements such as copper and silver; Group 12elements such as zinc; and Group 13 elements such as aluminum. Theexamples also include alloys of these metals (such as aluminum alloysand stainless alloys (stainless steels)), and compounds including thesemetals (exemplified by metal oxides such as silver oxide and aluminumoxide). The materials may include each of different metal componentsalone or in combination. Among the metal components, particularlypreferred examples are copper, silver, aluminum, and stainless steels.The shape of the fiber collector 14 is exemplified by, but not limitedto, plate, roller, belt, net, sawlike, wave, needle, and linear shapes.Among these shapes, plate and roller shapes are particularly preferred.Non-limiting examples of the laser light absorber 19 include metals andporous ceramics each coated with a black body. Non-limiting examples ofthe heat absorber 18 include black ceramics. The use of the equipment asdescribed above enables efficient production of the nonwoven fabric.

The bone fixation material according to the present invention may be notonly one produced by the above-mentioned production method, but also oneproduced through a press process in which a PEEK fiber nonwoven fabricis compression-molded as needed typically using a mold. The bonefixation material may also be an integrated assembly of multiple pliesof the nonwoven fabric as stacked and compression-molded (pressed).

EXAMPLES

The present invention will be illustrated in further detail withreference to several examples below. It should be noted, however, thatthe examples are by no means intended to limit the scope of the presentinvention.

Example 1

Polymer Sheet Preparation

A polymer sheet having a thickness of 0.1 mm was prepared in thefollowing manner. Sample chips of a PEEK, VESTAKEEP 1000G (trade name,supplied by Daicel-Evonik Ltd.) were extruded into a sheet using theLABO PLASTOMILL T-Die Extruder (supplied by Toyo Seiki Seisaku-Sho,Ltd.) with a T-die having a die width of 150 mm and a lip width of 0.4mm, at an extrusion temperature of 345° C. to 360° C. The extruded sheetwas coiled at a haul-off roller temperature of 140° C. and a coilingspeed of 1.0 to 2.0 m/min to yield the polymer sheet.

The prepared polymer sheet had a melt viscosity (400° C.) of 151 Pa·sand a degree of crystallinity of 12.7%, where the melt viscosity wasmeasured by a method mentioned below. The degree of crystallinity of thepolymer sheet was determined by a method mentioned below for determiningthe degree of crystallinity of PEEK fibers constituting the nonwovenfabric.

Polymer Sheet Melt Viscosity (400° C.) Measurement Method

The melt viscosity of the polymer sheet was measured at 400° C. and ashear rate of 121.6 s⁻¹, using a capillary rheometer, Capillograph 1D(trade name, supplied by Toyo Seiki Seisaku-Sho, Ltd.) with a jig havinga capillary diameter of 1 mm and a length of 10 mm.

Next, using the polymer sheet prepared by the above method, a PEEK fibernonwoven fabric was produced by the following procedure.

PEEK Fiber Nonwoven Fabric Production

The PEEK fiber nonwoven fabric was produced using the nonwoven fabricproduction equipment schematically illustrated in FIG. 3.

The laser source 11 of the equipment illustrated in FIG. 3 used hereinwas a CO₂ laser system (supplied by Universal Laser Systems, Inc.,having a wavelength of 10.6 μm and a power of 45 W, with air cooling,and having a beam diameter of 4 mm). The light-path controller 12 of theequipment illustrated in FIG. 3 used herein was one including a beamexpander with 2.5-fold magnification, a homogenizer (having an incidentbeam diameter of 12 mm (designed value) and an outgoing beam diameter of12 mm (designed value)), a collimation lens (having an incident beamdiameter of 12 mm (designed value) and an outgoing beam diameter of 12mm (designed value)), a cylindrical lens (plano-concave lens, f-30 mm),and another cylindrical lens (plano-convex lens, f-300 mm) disposed inthe specified sequence at predetermined positions. By passing throughthese light-path controllers, the spot-like laser light was convertedinto planar laser light 5 having a width of about 150 mm and a thicknessof about 1.4 mm and was applied to the band-like melt zone (edge) 6 a ofthe polymer sheet 6. In this process, the laser light was emitted at anoutput of 61 W/13 cm, the polymer sheet was fed at a feed speed of 6mm/min, and the potential difference between the electrode 17 and thefiber collector 14 was 6 kV/cm.

This gave a nonwoven fabric made of PEEK fibers having an average fiberdiameter of 0.7 μm. The PEEK fibers constituting the nonwoven fabric hada degree of crystallinity of 24.0%, as measured by a measurement methodmentioned below.

The produced nonwoven fabric was used as a bone fixation material. Thebone fixation material had an average pore size of 200 μm and a porosityof 60%.

Method for Measuring Degree of Crystallinity of PEEK Fibers ConstitutingNonwoven Fabric

The degree of crystallinity of the PEEK fibers constituting the nonwovenfabric was calculated from the amount of heat determined by differentialscanning calorimetry.

The differential scanning calorimetry (DSC) was performed using adifferential scanning calorimeter DSC Q2000 (supplied by TA) withalumina as a reference material in a nitrogen atmosphere at temperaturesin the range of 0° C. to 420° C. and a rate of temperature rise of 20°C./min.

On the basis of the amount of heat determined by the differentialscanning calorimetry, the degree of crystallinity was determinedaccording to the expression:

Degree of crystallinity (%)=[(Heat of fusion (J/g) of sample)−(Heat ofrecrystallization (J/g) of sample)]/(Heat of fusion of perfect crystal(130 (J/g))×100

Bone Fixation Material Average Pore Size Measurement

The bone fixation material according to Example 1 was cut to give across-section, arbitrary 30 or more pores viewed in an electronphotomicrograph of the cross-section were selected, the areas of theselected pores were measured, and the average thereof was defined as theaverage pore area S_(ave). Assuming that the pores are prefect circles,the average pore area was converted into a pore size (pore diameter)according to the following equation, and the converted value was definedas the average pore size. In the equation, π represents the ratio of thecircumference of a circle to its diameter.

Average pore size (μm)=2×(S_(ave)/π)^(1/2)

Bone Fixation Material Porosity Measurement

The porosity of the bone fixation material according to Example 1 wascalculated according to the following equation.

The volume and the weight of part or all (entire) of the bone fixationmaterial were measured, where the portion had been cut from the bonefixation material.

In the following equation, V represents the volume (cm³) of the bonefixation material; W represents the weight (g) of the bone fixationmaterial; and ρ represents the density (g/cm³) (the density of PEEK is1.27):

Porosity [%]=100−100×W/(ρV)

REFERENCE SIGNS LIST

1 laser source

2 beam-expander-homogenizer

3 collimation lens

4 cylindrical lens group

5 planar laser light

6 polymer sheet

6 a band-like melt zone

6 b needle protrusion

7 holder

8 fiber collector

9 thermography

10 high voltage generator

11 laser source

12 light-path controller

13 polymer sheet feeder

14 fiber collector

15 heating device

16 holder

17 electrode

18 heat absorber

19 laser light absorber

20 a high voltage generator

20 b high voltage generator

21 pulley

22 collection member

23 cabinet

h height of Taylor cone

w width direction

24 bone fixation material

25 bone

26 bone lesion area

As a summary of the above description, the configurations according toembodiments of the present invention, as well as variations thereof,will be listed below as appendices.

(1) A bone fixation material including a nonwoven fabric made of PEEKfibers.

(2) The bone fixation material according to (1), wherein the bonefixation material has an average pore size of 3 to 280 μm.

(3) The bone fixation material according to one of (1) and (2), whereinthe bone fixation material has a porosity of 15% to 70%.

(4) The bone fixation material according to any one of (1) to (3),wherein the PEEK fibers have an average fiber diameter of 10 μm or less.

(5) The bone fixation material according to any one of (1) to (4),wherein the nonwoven fabric has a mass per unit area of 10 to 100000g/m².

(6) The bone fixation material according to any one of (1) to (5),wherein the nonwoven fabric has a thickness of 0.05 to 100 mm.

(7) The bone fixation material according to any one of (1) to (6),wherein the PEEK fibers have a degree of crystallinity of 30% or less.

(8) The bone fixation material according to any one of (1) to (7),wherein the bone fixation material has a thickness of 0.05 to 100 mm.

(9) The bone fixation material according to any one of (1) to (8), whichis in the form of sheet or tube.

(10) The bone fixation material according to any one of (1) to (9),wherein the bone fixation material has undergone hydrophilizationtreatment (such as plasma treatment, graft reaction treatment afterplasma treatment, corona discharge treatment, glow discharge treatment,alkaline solution treatment, acid solution treatment, oxidizertreatment, silane coupling treatment, anodizing treatment, or rougheningtreatment).

(11) The bone fixation material according to any one of (1) to (10),wherein the PEEK fibers include PEEK in a proportion of 50 weightpercent or more.

(12) The bone fixation material according to any one of (1) to (11),wherein the bone fixation material has a density of 0.05 to 1.2 g/cm³.

INDUSTRIAL APPLICABILITY

The bone fixation material according to the present invention is usablein the medical field so as to repair, reinforce, and/or protect aninjury area typically of bone tissue, where the injury has been causedtypically by a disease or in an accident.

1. A bone fixation material comprising a nonwoven fabric made of PEEKfibers.
 2. The bone fixation material according to claim 1, wherein thebone fixation material has an average pore size of 3 to 280 μm.
 3. Thebone fixation material according to claim 1, wherein the bone fixationmaterial has a porosity of 15% to 70%.
 4. The bone fixation materialaccording to claim 1, wherein the PEEK fibers have an average fiberdiameter of 10 μm or less.
 5. The bone fixation material according toclaim 1, wherein the nonwoven fabric has a mass per unit area of 10 to100000 g/m².
 6. The bone fixation material according to claim 1, whereinthe nonwoven fabric has a thickness of 0.05 to 100 mm.
 7. The bonefixation material according to claim 1, wherein the PEEK fibers have adegree of crystallinity of 30% or less.
 8. A method for fixing a bonecomprising using a nonwoven fabric made of PEEK fibers.
 9. The methodaccording to claim 8, wherein a bone fixation material comprising thenonwoven fabric has an average pore size of 3 to 280 μm.
 10. The methodaccording to claim 8, wherein a bone fixation material comprising thenonwoven fabric has a porosity of 15% to 70%.
 11. The method accordingto claim 8, wherein the PEEK fibers have an average fiber diameter of 10μm or less.
 12. The method according to claim 8, wherein the nonwovenfabric has a mass per unit area of 10 to 100000 g/m².
 13. The methodaccording to claim 8, wherein the nonwoven fabric has a thickness of0.05 to 100 mm.
 14. The method according to claim 8, wherein the PEEKfibers have a degree of crystallinity of 30% or less.
 15. A method forproducing a bone fixation material comprising using a nonwoven fabricmade of PEEK fibers.
 16. The method according to claim 15, wherein thebone fixation material has an average pore size of 3 to 280 μm.
 17. Themethod according to claim 15, wherein the bone fixation material has aporosity of 15% to 70%.
 18. The method according to claim 15, whereinthe PEEK fibers have an average fiber diameter of 10 μm or less.
 19. Themethod according to claim 15, wherein the nonwoven fabric has a mass perunit area of 10 to 100000 g/m².
 20. The method according to claim 15,wherein the nonwoven fabric has a thickness of 0.05 to 100 mm.
 21. Themethod according to claim 15, wherein the PEEK fibers have a degree ofcrystallinity of 30% or less.